Method for joining dissimilar metal plates

Abstract

A method for joining two dissimilar metal plates having different volume resistivity with enhanced joint strength. The method includes overlaying a first metal plate made of first metal and a second metal plate made of second metal with higher volume resistivity and higher melting point in comparison with the first metal, bringing a pair of electrodes into contact with the surface of a portion of the second metal plate overlapping the first metal plate, supplying current between the electrodes so as to resistance-heat the second metal present in a current-flowing region to a temperature lower than the melting point of the second metal and higher than the melting point of the first metal, thereby partially melting the first metal plate with the heat so that an intermetallic compound is generated between the first and second metal plates, and thus joining the first and second metal plates via the intermetallic compound.

What is claimed is: 
     
       1. A method for joining two dissimilar metal plates, comprising:
 overlaying, as the dissimilar metal plates, a first metal plate and a second metal plate one on top of the other, the first metal plate being made of a first metal, the second metal plate being made of a second metal with a higher volume resistivity than that of the first metal and having a higher melting point than that of the first metal; 
 bringing a pair of electrodes into contact with a surface of a portion of only the second metal plate overlapping the first metal plate, without any electrodes contacting the first metal plate, wherein the pair of electrodes are arranged opposite each other with a space therebetween; and 
 supplying current between the pair of electrodes to create a current-flowing region within the second metal plate, so as to resistance-heat the second metal present in the current-flowing region to a temperature lower than the melting point of the second metal and higher than the melting point of the first metal, thereby partially melting the first metal plate with heat from the resistance-heated second metal, without melting the second metal plate, so that a melted portion of the first metal plate diffuses to a side of the first metal plate that faces the second metal plate, and so that an intermetallic compound of the first metal and the second metal is generated between the first metal plate and the second metal plate, and thus joining the first and second metal plates via the intermetallic compound, 
 wherein: 
 the bringing the pair of electrodes into contact with the surface of the portion of the second metal plate overlapping the first metal plate includes arranging a pressurizing member in the space between the pair of electrodes, the pressurizing member being made of a non-conductive material, 
 the joining of the first and second metal plates includes supplying current between the pair of electrodes while pressuring the second metal plate against the first metal plate using the pressurizing member arranged between the pair of electrodes, so as to push a portion of the intermetallic compound toward regions outside of an area of the melted portion of the first metal plate, and 
 during the step of joining the first and the second metal plates, the pressurizing member is pressurized against the second metal plate with a pressure higher than that of the pair of electrodes. 
 
     
     
       2. The method for joining two dissimilar metal plates according to  claim 1 , wherein the first metal plate is one of an aluminum plate or an aluminum alloy plate, and the second metal plate is a steel plate. 
     
     
       3. The method for joining two dissimilar metal plates according to  claim 1 , wherein the current is supplied between the pair of electrodes such that welding is performed so as to form a fresh surface on the second metal plate by diffusing the elements on the surface of the second metal plate. 
     
     
       4. The method for joining two dissimilar metal plates according to  claim 1 , wherein the second metal plate is not melted so as to positively pressurize the second metal plate. 
     
     
       5. The method for joining two dissimilar metal plates according to  claim 1 , the method further comprising cooling a surface layer of the first metal plate while cooling the pair of electrodes, after the current is supplied between the pair of electrodes. 
     
     
       6. The method for joining two dissimilar metal plates according to  claim 1 , wherein a surface of the first metal plate on a side thereof contacting a mount base is not melted due to the pressurization by the pressurizing member. 
     
     
       7. The method for joining two dissimilar metal plates according to  claim 1 , wherein the current supplied between the pair of electrodes is supplied while the second metal plate is in a solid-phase state, so that elements on the surface of the second metal plate diffuse to the first metal plate.